THE PRODROMUS 221 



internal fluid either take on the form of fibres (since they are 

 partly added through open pores along the length of the ex- 

 tended fibril, and are partly disposed in the interstices of the 

 fibrils into the form of a new fibril by the permeating fluid), or 

 form simple replacements: and in these two ways plants and 

 animals are formed^ Since I am less familiar with the anatomy 

 of plants, I do not decide whether there are present several 

 internal fluids ; but it is certain that in animals different inter- 

 nal fluids are to be found, and I shall try to reduce these to a 

 definite classification. 



Besides the attenuated fluid permeating all things, we note in 

 the case of animals at least three kinds of fluids, of which the 

 first is external ; the second is internal and common, the third 

 P. 20. an internal fluid peculiar to each part. By the term external 

 fluid I mean that fluid in animals which not only surrounds the 

 surface exposed to our eyes, as the atmosphere, but also that 

 which is in contact with all the remaining surfaces of the body 

 which are continuous with it through the larger foramina of the 

 surface, such as the entire surface of the trachea, with which the 

 air inhaled in breathing comes in contact ; the entire surface of 

 the alimentary canal, by which I mean the mouth, the oesopha- 

 gus, the stomach, and the intestines ; the entire surface of the 

 bladder, and of the urethra; the entire surface which com- 

 municates with the uterus, especially in the years of puberty ; 

 the entire surface of all the excretory organs from the capillaries 

 even to the orifices which discharge their contents into the 

 ears, eyelids, nose, eyes, alimentary canal, bladder, urethra, 

 uterus, and skin — a separate enumeration of which would show 

 that many are truly external which are commonly considered in- 

 ternal, nay, even internal in the highest degree, and hence it 

 follows : 



1. That worms and calculi are generated within our body 



and that most are formed in the external fluid. 



2. That many parts are essential to certain animals be- 



cause they have them, not because the animal cannot 

 exist without them. 

 A fluid which is in contact with these surfaces I call external 

 because it communicates with the surrounding fluid by means 



