12 Chapter I 



celebrated botanist Alexander Braun 1 issued his work on the genus 

 [14] Chytridium, in which he demonstrated the fact that certain plants 

 and flagellated Infusoria suffer from the invasion of a small mobile 

 parasite which, attaching itself to their body-wall, absorbs the 

 contents and so destroys its hosts, causing a very great mortality 

 among them. The cycle of development in the Chytridia, established 

 by Braun, left no doubt as to the accuracy of his view and even 

 renders it possible for us to interpret more accurately the earlier 

 observations of Stein, on the supposed evolution of certain Infusoria, 

 by showing that the changes observed in these organisms were in 

 reality due to an invasion by Chytridia. 



Since these observations were made it has been clearly demon- 

 strated that among the unicellular organisms, certain Flagellata and 

 ciliated Infusoria are subject to infective maladies the result of 

 parasitism of the Chytridiaceae, a group of the lower Fungi. Small, 

 mobile, colourless cells attach themselves to the surface of the 

 Protozoa, penetrate into their interior and absorb the greater part 

 of their living content. Sometimes these parasites multiply in a most 

 extraordinary fashion and destroy enormous numbers of the Infusoria. 

 Thus, Nowakowski 2 , who has given a very detailed description of 

 Polyphagus euglenae, the Chytridium of the common green fresh- 

 water Euglena, records the disappearance of the Euglenae from 

 his aquaria glasses : the parasites " were reproduced in such great 

 abundance that ultimately they had completely replaced the Euglenae." 

 The Flagellata, subject to infection by Chytridict, are found almost 

 exclusively amongst those genera (Cryptomonas, Chlamydomonas, 

 Haematococcus, Phacus, Volvox, etc.) which are nourished after the 

 fashion of vegetables, that is by the absorption of substances dissolved 

 in the surrounding fluids. It is very remarkable that in the group of 

 ciliated Infusoria this parasitism of the Chytridia is observed almost 

 solely in the encysted forms, that is to say, at a stage when the 

 animalcules, surrounded by their envelope, do not take any nourish- 

 ment. The invasion by the Chytridia has been demonstrated in the 

 case of the cysts of the Vorticellina, Oxytrichinina, Nassula, etc. 3 

 These facts indicate that the absence of the digestion of solid 

 aliments, such as occurs in almost all the ciliated Infusoria, con- 



1 "Ueber Chytridium," in Mcmatsber. d. Berliner Akad., 1855, June, No. 14. 



2 Conn's "Beitrage zur Biologic der Pflanzen," Breslau, 1876, Bd. n, S. 210. 



3 For the parasites of Infusoria, cf. Biitschli in Bronn's " Klassen und Ordnungen 

 d. Thier-Reichs," Leipzig, 18851889, Bd. i, SS. 872, 1823, 1944. 



