صور الصفحة
PDF
النشر الإلكتروني

been made, forty-two of which have reached full term and are recorded.

"From these forty-two matings, only seven young animals have survived, and five of them are unusually small, though their parents were large, vigorous guinea-pigs. The following combinations were made:

"1. Alcoholic males were mated to normal females. This is the paternal test, and is the really crucial proof of the influence of alcohol on the germ cells, since the defective offspring in this case must be due to the modified spermatozoa, or male germ cells, from which they arise. Twenty-four matings of this type were made, fourteen of which gave no result or very early abortions; five stillborn litters were produced, consisting of eight individuals in all, and five living litters containing twelve young. Seven of these twelve died soon after birth, and only five have survived. Four of the survivors are from one litter and the fifth is the only living member of a litter of three. "2. Normal males were mated with alcoholic females. This is the maternal test. In such cases the alcohol may affect the offspring in two ways-by modifying the germ cells of the mother or acting directly on the developing embryo in utero. Only four such matings were tried. One gave no offspring; three living litters were born, one consisting of three premature young that died at birth, while the other two litters consisted each of one young, which have survived. The alcoholic treatment in one of the last cases was only begun after the mother had been pregnant for about three weeks.

"3. Alcoholic males were mated to alcoholic females. This is the most severe test, both parents being alcoholic. Fourteen such matings gave in ten cases no offspring, or very early abortions. Three still-born litters were pro

duced, consisting in all of six individuals, while only one living young was born. This single offspring from the fourteen matings died in convulsions on the sixth day after birth.

"The young that have died in the experiment showed nervous disorders, many having epileptic-like seizures, and all died in convulsion.

"Nine control matings in the same group of animals have given nine surviving litters, consisting in all of seventeen individuals, all of which have survived and are large, vigorous animals for their ages. Two young from nonalcoholic parents died, but this mother also died two days later. Her diseased condition doubtless affected the suckling young.

"Forty-two matings of alcoholic guinea-pigs have given only eighteen young born alive, and of these only seven, five of which are runts, survived for more than a few weeks, while nine control matings have given seventeen young, all of which have survived and are normal, vigorous individuals. These facts convincingly demonstrate the detrimental effects of alcohol on the parental germ cells and the developing offspring." 13

A few years ago, Paul Kammerer of Vienna, a believer in the inheritance of acquired characters, made some striking claims of the changes he had been able to produce in the midwife toad and the fire salamander. "The fire salamander, which lives in moist woods has become a favorite of mine. If kept for several years upon yellow clay then his yellow markings become enriched at the expense of the black ground color. If half of the offspring of individuals which have thus become very yellow be

13 STOCKARD, C. R. Racial Degeneration in Mammals Treated with Alcohol. Arch. Int. Med., Vol. X, No. 4, p. 369 ff.

raised on yellow soil, the amount of yellow increases and appears in broad regularly distributed longitudinal bands. The other half of the offspring if grown on dark soil becomes less yellow.

[ocr errors]

"If the parent generation of the fire salamander be raised on black garden soil after some years it becomes largely black, while the young kept upon black soil have a row of small spots on the middle of the back. On the other hand, in young which in contrast with their parents have been raised on yellow soil, these spots fuse into a band.

"If we use yellow paper instead of yellow soil and be gin our experiment, as we did before, with scantily spotted individuals, then we obtain enlargement, but no increase in the number of the spots. If we take black paper, then we obtain a reduction in the size of the spots without reduction in intensity of coloration. The young bear the few spots in the middle, while the normal young from the control brood in mixed surroundings at once produce an irregular pattern of markings.

"Heavy moisture produces an increase of the yellow, but only in the number of the spots, none in the size of the spots. Numerous but still small spots may be observed in the progeny put back into the less moist surroundings. Comparative dryness results in loss of brilliancy but not in loss of size in the spots. The same phenomenon may be observed in the progeny which is again kept moist, especially when compared with the control brood which was kept under uniform conditions.” 14

Kammerer is convinced that he has here a case of the inheritance of acquired characters. It is however possi

14 KAMMERER, P. Adaptation and Inheritance. Annual Report of Smithsonian Institute, 1912, p. 435 ff.

ble, assuming the reliability of the statements, that this animal is in some way so susceptible to environmental influence that slight changes therein produce changes in its development or else that the germ cells are directly affected by the changes in the light and thus modified. Bateson, however, after a long review of Kammerer's work, says:

"I have felt obliged to express serious skepticism as to the validity of nearly all the new evidence for the transmission of acquired characters. At the present time the utmost we are bound to accept is the proof that (1) in some parthenogenetic forms variations, or perhaps we may say malformations, produced in response to special conditions, recur in one or perhaps two generations asexually produced after removal to other conditions. (2) That violent maltreatment may in rare instances so affect the germ cells contained in the parents as to cause the individuals resulting from the fertilization of those cells to exhibit an arrest of development similar to that which their parents underwent.

"As a contribution to genetic physiology these facts are very important and interesting, but I cannot think that any one, on reflection, will feel encouraged by such indications to revive old beliefs in the direct origin of adaptations." 15

By subjecting the eggs of the common potato bug to unusual conditions Tower has been able to effect changes which seemingly become hereditary. Other experimenters by using X-rays, radium and other substances have considerably modified certain amphibia. All these however are direct modifications of the germ cell and are not in the class of body cell changes which subsequently are 15 BATESON, W. o. c., p. 234.

alleged to be reflected in the nature of the germ cell. Without assuming a dogmatic position on the subject it seems that we must conclude that the germ cells are ordinarily protected from outside influences. Some of the reluctance to accept this conclusion is doubtless due to the realization that it takes away the basis of much of the old moral teaching. If goodness and badness do not cause physical success or deterioration, what does? Into this discussion we cannot enter now. We must merely state that many things once considered part of the physical heredity are henceforth to be grouped under social heredity; that is, are environmental problems. Each generation transmits to the succeeding the race-stuff of which it is the temporary custodian. This newer knowledge will require some restatement of our ideas. When we know that the single cell divides into two, each sharing the essential elements of the older cell, which shall we consider the daughter, which the mother? Biologically this is our relationship to our parents. They are our elder brothers and sisters, they and we alike, "chips of the old block."

In earlier days it was assumed that the germ cells contained a miniature of the mature organism, like it in all details save size. Now that we know something of its makeup we know that this idea is too naïve. Instead of some "homunculus" in the human germ cell, we must imagine a great number of units of some sort possessing the possibility under favorable conditions of developing into the adult. It taxes our credulity to see how the human spermatozoon whose length is about one-twentieth of a millimeter, combined with the egg which is about one-fifth of a millimeter in diameter- just about visible to the naked eye - not merely may develop but already

« السابقةمتابعة »