484 ORREN LLOYD-JONES AND F. A. HAYS 
be maintained, they rapidly cease this type of motion and become 
‘bunters’ or ‘spiral movers.’ 
But the fact that the velocity of any sperm which are showing 
progressive vibratile motion is as great in the latter services as in 
the earlier ones, considered by itself, does not give a true picture 
of conditions. For in semen from the earlier services the num- 
ber of sperm which display this type of motion are more numer- 
ous. In specimens from the later services it was often neces- 
sary to search over numerous fields before a satisfactory num- 
ber of progressive movers could be observed; in fact, as the table 
shows in actually one-half of the cases of 20th service, no sperm 
of this sort were discovered. 
The statements quoted from Iwanoff and Stigler to the effect 
that in semen from heavily taxed males the motion is ‘feeble’ or 
shows ‘little energy’ do represent the general impression that 
would result from an examination of such material. But. it 
seems this picture is not the result of a slowing down of the 
forward motion so much as the assumption of different types of 
motion, such as energetic ‘bunting’ motion, slow undulatory or 
rotary motion. 
DURATION OF MOTION 
The duration of motion of spermatozoa both in the female 
genital tract and outside the body under laboratory conditions 
has received greater attention from writers than any other phase 
of study about spermatozoa. Unless sperm show continued ac- 
tivity for several hours within the female genitalia, they never 
take part in fertilization. The published facts in regard to the 
length of time sperm may retain their fertilizing power within 
the body of the female and motility in vitro are numerous and 
not always in harmony with each other, and no attempt will be 
made to review them here. Semen held in vitre will withstand 
a wide range of temperatures. Mantegazza (Iwanoff, p. 493) 
asserts that mammalian sperm retain vitality between —15°C. 
and 47°C., and Iwanoff himself carried semen of horse to a point 
where it solidified (ca. —15°C.) without destroying motion when 
the temperature was raised, but the same author does admit 
