Chap, i.] MALE ORGANS. 1115 



the movements of a spermatozoon, like ciliary movements, are 

 favoured by fluids having a weak alkaline reaction, whereas 

 almost any degree of acidity (unless used to neutralize exces- 

 sive alkalinity) arrests them ; and the mucous secretion of the 

 uterus while it is alkaline at the neck of the uterus becomes 

 acid as it passes down the vagina. Hence it might be inferred 

 that those spermatozoa only which rapidly find their way into 

 the os uteri manifest vigorous movements ; but it would be dan- 

 gerous to lay too great stress on this. 



§ 689. The semen contains a relatively large quantity of 

 solid matter, and this in turn is to a great extent furnished by 

 the spermatozoa ; indeed the spermatozoa form so large a por- 

 tion of the semen that the chemical substances present in the 

 former are dominant in the latter. The head of a spermatozoon 

 appears to be largely composed of the body or group of bodies 

 known as nuclein or nucleo-albumin, a result which supplies 

 chemical evidence of the nuclear nature of the spermatozoan 

 head ; and nuclein forms a considerable portion of the solid 

 matter of the whole semen. Lecithin is also present in the 

 semen in considerable quantity ; otherwise the chemical features 

 of the secretion, which are as yet imperfectly known, present no 

 special interest. The crystals found in dry semen are not as was 

 once thought of a proteid nature but are compound phosphates 

 containing an organic base. As discharged in coitus the semen 

 proper from the testicle is mixed with the prostatic and other 

 secretions. 



From the testicle itself various forms ' of proteid of the 

 globulin class have been extracted ; and glycogen is not unfre- 

 quently present. 



The cavity of the vesicula seminalis serves as a temporary 

 receptacle for the semen, though some secretion, and in some 

 animals a decided quantity, takes place from its interior. In 

 certain animals the secretion clots, and then appears to contain 

 a substance identical with or allied to fibrinogen ; in these ani- 

 mals the clot which is thus formed by the mixture of the male 

 secretion with the bloody secretion of the rutting female helps 

 to secure the retention of the former within the female passages. 

 The secretion of the prostate presents no special features, except 

 that it is apt to contain peculiar concentric corpuscles ; but the 

 fact that the prostate remains undeveloped in castrated animals 

 suggests that the secretion plays some part in coitus. The 

 glands of Cowper afford a thick mucous secretion. 



§ 690. Erectile Tissue. The erectile tissue of the corpora 

 cavernosa and corpus spongiosum consists of an irregular laby- 

 rinth formed by trabeculse composed of connective tissue with 

 abundant elastic elements mixed up with a large but variable 

 amount of plain muscular tissue. The spaces of the trabecule 

 are lined by spindle-shaped epitheloid plates, resting in some 



