12 ON PARASITES. 



first part of the experiment tlie invisible spores and ovules in the air 

 sucked through the tubes were exposed to the action of the acid and 

 alkali, and killed. In the latter part, the air freighted with the in- 

 visible germs came in direct contact with the infusion, and those 

 germs finding there a suitable nidus for development, gave origin to 

 the living beings witnessed. If then it is established that each one 

 of us breathes an air laden with the germs of organisms that only 

 want a nidus for development ; that with the food we eat, and es- 

 pecially the water we drink, additional germs are introduced into 

 our system by another channel ; if as we know positively by abundant 

 observation, we ourselves as well as the lower animals and plants 

 are the actual habitat of parasites ; let us by all the means at our 

 command, ascertain the conditions of existence and ways of life of 

 those beings, that as far as possible the material well-being of our 

 race, and the interests of natural science may be promoted. The dis- 

 cussion that is still open as to the origin of niimerous cutaneous dis- 

 eases demonstrates the necessity of eliminating all causes of error from 

 investigations of such obscurity. Gruby, Grulliver, and other careful 

 observers positively maintain the parasitic origin oi porrigo favosa. 

 Wilson in an article, every page of which is the expression of careful 

 researches, denies the presence of any cryptogam in the crust, and 

 shows that the first named observers were misled by deceptive ap- 

 pearances. Both parties thus investigate the same result but trace 

 it to different causes. 



The vastness of the obscurity which rests upon the subject of para- 

 sites naturally leads to much speculation. Facts here as elsewhere 

 are made the basis of undue generalization. 



The domain of reason which is the result of experience lies beside 

 that of imagination, and many avenues lead from one into the other. 

 The ascertained fecundity of parasites, the new species continually 

 discovered in the most unexpected places with the various morbid 

 symptoms which they are Jcnown to cause, easily lead to the supposi- 

 tion of the parasitic origin of diseases which really arise from other 

 causes. Thus with the growth of natural science do its requirements 

 for additional investigation augment. Questions are perpetually re- 

 opened that were once supposed to be definitely settled, and new ones 

 are raised. Erom each rugged summit upon the hill of science that 

 its devotee attains, he sees others still more diScalt of access rising 

 above him. Bat still he struggles on although often with naught but 



