INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 247 



remain so. On the other hand Do Bary has made known the life- 

 history of some simple fungi which destroy insects, and from Pasteur, 

 Cohn, and others we know of diseases due to tliose simplest of fungi, 

 the Bacteria, which produce the most deadly ravages amongst insects. 

 Professor Metschnikoff has examined some of these minute parasitic 

 fungi and cultivated them by passing them from one insect to another, 

 and has experimentally proved their very deadly character to the 

 insects exposed to infection. The " green muscardine " (Isaria de- 

 structor) is the name given by Metschnikofl' to one of the minute 

 fungi the eflects of which he most successfully traced. Now it is 

 perfectly evident that if green muscardine spores could be produced in 

 large quantity, or spores of similar disease-producing fungi, and 

 applied to the ground and shrubs infested by insect pests liable to 

 harbour those fungi, we should have the best of all means for effect- 

 ing the destruction of the insects, viz. a poison which once set at 

 work would spontaneously multiply and spread its destroying agents 

 around. 



Accordingly Professor Metschnikoff endeavoured to cultivate the 

 "green muscardine" apart from insects, so as to obtain its sj^ores if 

 possible in great quantity, in a liquid which might be applied to 

 places attacked by injurious insects. He at last succeeded in effect- 

 ing this cultivation by the use of beer-mash : in this decoction the 

 green muscardine produced a rich mycelium and finally spores. 



It is exceedingly probable that we have here the true explanation 

 of the value of the application of yeast to plants, &c., affected by 

 insect pests. If there are a few spores only of such parasites as the 

 " green muscardine " about, the fluids of the yeast will serve them for 

 nourishment and so cause the muscardine to spread until it comes into 

 contact with the insects. There is no reason to suppose that the 

 beer-yeast plant itself is capable of generating a disease in any 

 insects, at tlie same time we must remember that yeast as ordinarily 

 used by the brewer is by no means pure ; it contains in small quan- 

 tities other minute fungi besides the Saccharomyces cerevisiw, and it is 

 quite possible that a given quantity of it, say a pint, may, if the 

 brewery from which it came were not conducted on the most perfect 

 system (such as that lately introduced by Pasteur), contain a few 

 spores of such a disease-producing parasite as muscardine. A 

 diseased insect once in a way falling into the mash-tub would suffi- 

 ciently keep up the supply, and thus it is possible that yeast may 

 carry infection to insect pests and destroy them. 



At the same time Professor Mctschnikoff's suggestion of a delibe- 

 rate cultivation of an insccts'-disease-producing fungus, and the apjili- 

 caticm of the cultivated fungus in quantity to places infested by these 

 insects, is in the highest degree ingenious and likely to give results 

 the value of which will be estimated in thousands of pountls, and so 

 do something to persuade " practical " men that all science (biology as 

 much as chemistry, geology, or electricity) is deserving of their 

 respect and encouragement. 



MM. Brongniart and Cornu have also presented a note * to the 



* ' Cuinptis Keiidus," xc. (1880) p. 2V.K 



