MODERN BIOLOGY 549 



allowing this specimen to reproduce itself there came into being a "pure 

 line" of yeast-fungi, possessing fully controllable characters. This technique 

 of yeast-cultivation has entirely reformed the brewing industry and the 

 manufacture of yeast. Moreover, Hansen has added much of value to our 

 knowledge of the enzvmes, which play an active part in fermentation phe- 

 nomena, and a number of other kindred manifestations. A new conception 

 of the process of fermentation has been produced by Eduard Buchner (1860- 

 1917), professor of chemistry at Berlin. He has proved that the alcoholic 

 fermentation of sugar is not, as was hitherto believed, caused directly by 

 vital action on the part of the yeast-fungi, but that these organisms produce 

 a chemical ferment which brings about the yeasting and which can be iso- 

 lated and made to function even in the absence of the fungi. As a result of 

 this discovery the classical fermentation-theory set up by Pasteur has been 

 considerably modified and has been transferred from the sphere of biology 

 to that of chemistry. A number of other phenomena in the same category will 

 be discussed later on in this work. 



Of far later date than the knowledge of bacteria and yeast-fungi is our 

 knowledge of another group of organisms, which are usually referred to 

 the animal kingdom and which have been found to resemble bacteria in 

 being producers of disease — namely, the Sporozoa. Even Meckel was aware 

 that the well-known disease "ague," or malaria, was accompanied by a 

 peculiar darkening of the blood corpuscles and of certain other tissue ele- 

 ments in the infected subjects. But the disease itself was considered to be 

 "miasmatic" — that is, due to poisonous vapours emanating from the hu- 

 mid districts in which it occurs. Then the French army surgeon Alphonse 

 Laveran (1845-19x0, while serving in Algeria in 1880, discovered that the 

 said pigmentation is caused by a parasite which occurs under various forms, 

 but which, owing to its mobility, he thought belonged to the animal king- 

 dom. His accurate description of the newly-discovered producer of disease 

 was worthy of the closest attention, but it threw no light on the causes 

 of its distribution. This point was definitely answered by the Englishman 

 Sir Ronald Ross, who was born in 1857 in India, where he was serving as 

 an army surgeon, and who was afterwards elected to a professorial chair at an 

 institute of tropical diseases at Liverpool. He discovered the alternation of 

 generation in the malarial plasmodium: how, after developing in the human 

 blood, it is absorbed by blood-sucking mosquitoes, is conveyed from the 

 mosquito's intestinal canal into its salivary glands, and thence passes into 

 the blood of human beings, who thus become likewise infected. An impor- 

 tant contribution to the problem of malaria has been made by the Italian 

 Giovanni Baptista Grassi (1854-19x5), professor of zoology at Rome, who 

 made his name especially on account of the effective measures of protection 

 he adopted against malaria in his own country, which was so terribly 



