352 



SCIENCE. 



[N. S. Vol. XIX. No. 478. 



fifteen or twenty-minute periods were used 

 instead of ten-minute periods. 



Fertilization of the eggs was accomplished 

 in the following manner : The tube marked X 

 was pushed down into the sperm. The latter 

 was, therefore, immediately forced over by 

 the air pressure and mixed with the eggs. 

 Fertilization was usually very perfect and 

 cleavage, so far as I could determine, went on 

 in a normal way, provided sufficient air was 

 forced through. In one experiment the cur- 

 rent of air equalled 25 c.c. per minute. One 

 difficulty experienced was the maintenance of 

 a uniform current. This is a possible source 

 of error. 



The experiment was continued usually about 

 two hours, or over two or three cleavages. In 

 one case it was continued until swimming 

 blastulse had formed. 



It will be noted that tubes ' ' contained the 

 C0„ produced by both the sperm and unfertil- 

 ized eggs during ten minutes. A single trial 

 indicated the probability that the larger pro- 

 portion of CO, was due to the sperm, probably 

 because of their motility. Tubes ' 1,' on the 

 other hand, contained the 00^ produced in 

 ten minutes by the fertilized eggs and the 

 unused sperm. 



It is, therefore, plain that no accurate com- 

 parisons of the 00, production of unfertilized 

 and fertilized eggs, and no measurement of 

 the CO. produced by the eggs in either condi- 

 tion, can be made tintil the CO^ production of 

 the sperm has been ascertained. This has not 

 yet been done. 



The results so far apparent may be briefly 

 stated. It appeared in nearly all the experi- 

 ments that an increase in CO^ production oc- 

 curred in the first ten- or fifteen-minute in- 

 terval following fertilization. The increase 

 was slight and sometimes could not be detected. 

 Following this came an interval in which the 

 CO. production was small, visibly less, indeed, 

 in two or three experiments than that of the 

 unfertilized eggs and sperm. This is the mid- 

 period of cleavage, approximating, perhaps, 

 the time of nuclear growth and the early stages 

 of karyokinesis. 



The interval during which the eggs were 

 actively dividing into the first two blastomeres 

 (say 45 to 60 minutes after fertilization) was 



one of active CO^ production. In nearly every 

 experiment the barium hydrate tubes for this 

 time became markedly turbid as compared with 

 any others. After this period of greater COj 

 production came an interval of lessened pro- 

 duction. In one or two cases a second rise 

 occurred at about the time of the second 

 cleavage. Presumably a regular pendulum 

 swing of increased and decreased CO, produc- 

 tion occurred in the successive cleavages. 



If this rhythm proves, on further investi- 

 gation, to be constant, we have in the segment- 

 ing egg an interesting demonstration of the 

 principle that oxygen consumption and COj 

 production are not parallel and concomitant 

 processes. Pasteur's yeast experiment shows 

 well that abundant oxygen leads to synthesis 

 and growth, and little CO^ is excreted. Lack 

 of oxygen, on the other hand, means fermenta- 

 tion and a large production of gas. In my ex- 

 periments the time of maximum oxygen need 

 was apparently one of only moderate 00^ pro- 

 duction, while the period of maximum CO, 

 production was really the period of least de- 

 mand for oxygen. In other words, the COj 

 produced in cleavage seems to be largely the 

 result of splitting or fermentative processes 

 and not of direct oxidation. 



Another fact clearly indicated was the in- 

 crease in COj production as development pro- 

 gresses. By the time the eggs have reached 

 the blastula stage, even before they begin to 

 swim, they produce much more CO, per hour 

 than in earlier stages. 



An effort was made to determine the CO^ 

 production quantitatively. At Dr. Mathew's 

 suggestion the BaC03 in tube F was allowed 

 to settle ; measured samples of the supernatant 

 liquid were drawn off and titrated with m/20 

 oxalic acid. Phenophthalein was used as an 

 indicator. Enough was done to indicate the 

 applicability of "the method. 



As indicated earlier in the paper, I do not 

 consider the results so far obtained conclusive. 

 But by the application of refined methods the 

 problem can be solved. I hope at some future 

 time to work out a modification of Blackman's* 

 or Fletcher'sf apparatus which may be appli- 



* Blaekman, Philosophical Transactions, Vol. 

 186, 1895. 



t Fletcher, Jour, of Physiol., Vol. 23, 1898. 



