560 MANUAL OF HISTOLOGY. 



284. 



In the foregoing section a microscopical analysis of the contents of the 

 seminiferous tubes in the state of rest, not of activity, has been presented 

 to us. During the whole period of virility in man, however, and in the 

 rutting season of animals, these glandular tubes generate another kind of 

 contents, namely, semen or spermd). 



Human semen, as secreted by the testis, is a whitish slimy fluid desti- 

 tute of any odour, and of high sp. gr. Its reaction is either neutral 

 or alkaline. Semen, however, as discharged in coitu, has received addi- 

 tions from the accessory glands of the generative organs, and so undergone 

 considerable modification. It reacts strongly alkaline, and has a peculiar 

 odour, which has been aptly compared to that of freshly sawn bone. 

 Besides this, it is more fluid and transparent. Shortly after being ejected 

 it coagulates, forming a thick gelatinous mass, which becomes again liquid 

 after some time. 



A glance at fresh human semen under the microscope shows innumer- 

 able thread-like form elements engaged in the most lively motion. To 

 these several names have been given, such as seminal filaments, seminal 

 animalcules, and spermatozoa (fig. 548). Suspended in a homogeneous 

 fluid they are seen to consist of two portions, namely, an anterior wider 

 end known as the head ; and a long filiform process posteriorly, to which 

 the term tail has been applied. 



The form of the head (a) is oval, or, more correctly speaking, pear- 

 shaped ; the broadest end being posterior, at the insertion of the tail. Its 

 length is, on an average, 0-0045 mm., and its breadth 

 about half as much. When the head is seen in 

 profile (&), we remark that, like the corpuscles of 

 the blood, it is greatly flattened. Seen from the 

 surface it appears broad, with sharp but not dark 

 outline, but viewed from the side it is narrow, and pre- 

 sents a broad dark border. Its thickness lies probably 

 somewhere about 0-0018-0-0013 mm. (Koelliker). 

 The hindermost division of the structure, the fili- 

 form process (, b) commences with a constricted 

 neck, succeeded by a somewhat thickened por- 



ae 



broad surface; 6, in pro- tion, gradually becoming thinner and finer, until at 



last it attains such a pitch of tenuity as to baffle 



microscopic analysis. It may be followed to a length of about 0'0451 mm. 



For a long time it was supposed that the spermatozoa only consisted of 

 these two parts, and that they were quite homogeneous throughout, 

 without any distinction between envelope and contents, More recent 

 observations, with the aid of the stronger systems of lenses of the present 

 day, would seem to place this view in question. The reports, however, 

 of Valentin, Grohe and Schiveigger-Seidel on the subject do not yet 

 entirely agree. 



From the able researches of the last-named observer it would appear 

 that the tail of the spermatozoon (fig. 549) may be divided into two por- 

 tions, often sharply defined one from the other, and different in diameter 

 and in chemical and optical characters : these are, first, the middle 

 portion (&), as it is called ; and, secondly, the delicate terminal filament 

 (c). In those instances in which the head of the human spermatozoon 

 possesses the length mentioned above, of 0-0045 mm., the middle portion 



