Hair in its Microscopical and Medico-Legal Aspects. 169 



cortical substance being only a tbin layer ; often, indeed, is reduced 

 to a hem-like streak. This predominance of the medullary sub- 

 stance is seen best in the shaft of the hair ; toward the end the 

 cortical substance predominates, the medullary becoming thinner. 

 Generally, the cortical substance has the same structure as in 

 human hair, and the same variety of pigmentation ; in some 

 animals, as the cat, rat, and mouse, the cortical substance is more 

 translucent and of finer structure, resembling, under the microscope, 

 a hyaline envelope of the medullary substance. 



The medullary substance in animals is an interesting study, 

 differing greatly from the same layer in human hair. The cellular 

 structure is generally very evident, without the employment of any 

 reagent. The cells vary greatly in size and form. 



Though the hair of animals usually is so different from human 

 hair that it can be easily recognized, yet the difference is sometimes 

 less marked ; especially may this be the case with single hairs, and 

 at times only a single hair can be had for examination. This 

 resemblance is caused by the absence of the medullary substance. 

 Dogs' hair, especially when brown, is often very similar to human 

 hair, or may be almost exactly the same ; fortunately, only separate 

 hairs are thus similar, while generally the remaining hairs which are 

 given for examination have clearly the animal type. Keagents will 

 often help to decide the question. 



In medico-legal cases, when it has been decided that the hair 

 examined is human hair, the question arises, from whom it comes 

 and from what portion of the body. In regard to the first question 

 it may be merely said here that the hair examined must be compared 

 with that of the person concerned, both in regard to its gross 

 appearances and microscopically. 



In deciding to what part of the body the hairs belong, the length, 

 the size, the form, and the root of the hair, must be noticed. 



The hair from the head and beard is less limited in its length 

 than the hair on other portions of the body; though individual 

 and other circumstances may modify the length of the hair from the 

 head and the beard. 



The size of the hair differs in different parts of the body, and 

 so may form a diagnostic mark. The beard is the thickest generally, 

 measuring ' 14 to * 15 mm. Next comes the hair about the 

 female genitals, • 15 mm.; then the eyebrows, 0*12 mm.; the 

 hair about the male genitals, - ll mm.; finally, the hair from the 

 head in either sex, • 06 to • 08 mm. The great individual differ- 

 ences which are found may render the value of the size for diagnosis 

 less valuable. Moreover, it must not be forgotten that the same 

 hair may vary in diameter. The shape of the hair modifies its 

 diameter ; thus cylindrical hair especially is found only on the 

 head ; but when this is curly it is flattened, and the transverse 



