DISEASES OF THE DIGESTIVE OKGAJNB. 165 



require the operation of certain forces, in order that their peculiar 

 vital properties shall be manifested. They all require food, water, 

 and oxygen — food for the development of organized tissues, 

 water to maintain an equilibrium between the solids and fluids, 

 and oxygen for promoting various changes, uniting some particles 

 for the benefit of the whole fabric, and disengaging others destined 

 for excretion. These have to be obtained under various circum- 

 stances. The number of the different species of reptiles known 

 to naturalists is about 1,300, and there are at least 160,000 species 

 of insects. Among this vast assemblage of animate forms, a great 

 proportion obtain food, water, and oxygen in a situation and at a 

 temperature which is most congenial to each species, each one of 

 which, as species, exhibit great varieties in physical organization 

 and habits ; and hence the necessity for that diversity in geograph- 

 ical distribution which seems to surprise some men. Each species 

 of animal and insect carry about with them, in their own organi- 

 zation, the fertile embryonic habitation for successive parasitic 

 development, and all are, to a certain extent, dependent on each 

 other for both food and life. It has been truly said that there 

 " is life within life." Begin with the body of man, for example, 

 and we shall find that it is infested with thirty-nine distinct spe- 

 cies of entozoa. These are not confined to a single location, as 

 the bots to the digestive cavity of the horse ; but some are to be 

 seen in the eye, bronchial glands, kidneys, liver, gall, bladder, in- 

 testines, muscles, and even in the blood. There are several other 

 species of entophyta, to the number of ten, inhabitants of the skin 

 and mucous surfaces. So that the master can boast of a larger 

 number of living parasites within and about his body than we 

 have yet been able to find in his servant, the horse. And if the 

 former can carry about in the living citadel such a myriad of liv- 

 ing, active creatures, without inconvenience, and he being the 

 weaker party, why should not the horse, who is stronger, be able 

 to furnish nutriment for some half dozen or more bots that are 

 occasionally found in his stomach, and to perform his 2.40 gait 

 without inconvenience? Some of the inferior orders of creation 

 are the receptacle of a still greater amount of parasites. The 

 grasshopper, for example, is infested with a species of gordius, a 

 sort of hair-worm, which some persons have erroneously supposed 

 to be a transformed horse-hair. Several of these coil themselves 

 into the digestive cavity of the former, at times penetrating the 



