538 PHILOSOPHICAL TRANSACTIONS. [aNNO 1789. 



It will perhaps have some Influence in removing the prejudices against this 

 opinion, to make the following remarks. Hair is occasionally formed in parts of 

 the human body, which are absolutely unconnected with generation. Encysted 

 tumours are sometimes found containing hair. Mr. Hunter has a preparation of 

 this sort in his collection, which he cut out from under the skin of the eyebrow. 

 This tumour was perfectly complete, and unconnected with the skin, except by 

 the common intervention of cellular membrane, so as to have no communication 

 whatever with the hair of the eyebrow. In this instance there was certainly a 

 species of generation taking place in the encysted tumour itself, forming hairs as 

 completely and fully as in the common progress of the formation of a child. Such 

 encysted tumours have been found in other parts of the human body, and still 

 more frequently in quadrupeds. Mr. Hunter has in his collection many speci- 

 mens of encysted tumours from cows and sheep containing hair and wool. These 

 were perfectly complete, so as to have possessed a power of production within 

 themselves, and were many of them found deeply seated at a considerable distance 

 from the skin, which is the common parent of hair. In these tumours there is 

 often the appearance of layers of cuticle, which is probably a preparatory step to 

 the formation of hair. All this shows most clearly, that hair may be formed 

 without any species of generation as it is commonly understood. But hair is in 

 itself as distinct a consequence of generation as teeth, and as much a peculiar 

 substance. If then the one be formed, there appears to be no reason why the 

 other should not also be formed. The action producing the one is not better 

 understood than that producing the other ; nor does it appear to be really in it- 

 self less connected with that species of generation arising from the approach of a 

 male, so that teeth may probably be formed by a peculiar action taking place in 

 the ovarium itself, as well as the hair. 



It will tend to add further weight to this opinion, to consider that many of the 

 adult teeth are formed in a child after birth ; and therefore their formation de- 

 pends on an action taking place in the jaws at a particular period, and not on 

 original growth. The same circumstance strikes more strongly in the occasional 

 formation of teeth at an advanced time of life. Both of these processes take 

 place after the animal has been formed, in consequence of a certain action being 

 excited in a particular part of the body, and therefore there is less difficulty in be- 

 lieving that the same sort of process may go on in another part of the body not 

 commonly employed in it. It seems reasonable also to suppose, that the ovaria 

 should have a greater aptitude of taking on a process somewhat similar to genera- 

 tion than the other indifferent parts of the body, as they constitute a part of the 

 organs which are so materially concerned in the real process itself*. These cir- 



* As the formation of teeth and hair involved in a fatty mass may be said to be peculiar to the 

 ovaria, and as there are strong reasons for believing that this formation may take place without an in- 



