158 
ZOOLOGY: F. R. LILUE 
second place the original 1% sperm suspension was shown in several ex- 
periments to be capable of fertilizing a high percentage of eggs at 1 /30,000 
dilution or less, after a longer interval of time. If the sperm suspensions 
lose their fertilizing power with time, it must be that the significance of 
time in this respect varies inversely to concentration. 
This conclusion was abundantly verified by the following tests: A 
quantity of sperm suspension of a given concentration is prepared and 
divided in several equal amounts in a series of crystals; the same quan- 
tity of eggs is then added at time intervals to the crystals of the series, 
and the percentages of fertiHzation estimated by careful counts. Four- 
teen different grades of dilution between 1/300 and 1/240,000 of 1% 
sperm were thus measured. Loss of fertilizing power was shown in all 
of the suspensions thus tested in less than one hour; and in general the 
rate of loss increased with each successive dilution. The actual data 
are to be published elsewhere. Here we may simimarize the results in 
the following table, showing the approximate time required A, for 66% 
loss of fertilizing power, B, for complete loss, at six different dilutions. 
Dilution of sperm l/12oO% 1/3000% 1/6000% 1/30000% 1/60000^7 1/120000% 
A. 66% loss 32 min. 7 min. 5 min. 3 min. 2-3 min. 1 rain. 
B. 100% loss 64 min. 24 min. ? 20 min. 20? min. 7 min. 
Suspensions of higher concentrations, than those included in the table 
exhibited a much slower rate of loss, which was measured by another 
method, showing that from 1 /4% down, loss occurs in increasing amount 
within a period of 100 minutes. 
Other possible factors than time influencing the fertihzing power of 
sperm suspensions are on the whole relatively slight in this series of ex- 
periments. There is a certain natural variation in different lots of ova 
and sperm, which is no doubt responsible for some irregularities in the 
data. Another factor is that of egg-concentration; but a series of de- 
terminations showed that the actual variations due to this cause, occur- 
ring in the experiments themselves, are not of significance. 
There are two modes of explanation of these results theoretically pos- 
sible, viz : First, that the loss of fertilizing power is due to loss of motility 
of the spermatozoa; in the first place this theory does not agree with 
the observation, that the spermatozoa lose their fertiHzing power before 
they lose their motility; in the second place it renders the increase of 
rate of loss with dilution incomprehensible because on a priori groimds 
the exact opposite would be expected; in the third place as a result of 
several lines of work the theory that the fertilization reaction is primarily 
a function of motility of the spermatozoon has been given up; penetra- 
