ZOOLOGY AND BOTANY, MICROSCOPY, ETC. ' 303 



refrangible rays were the most active. In the course of the induction 

 which led to this conclusion two other facts of importance were 

 elicited. The molecule of oxalic acid was speedily resolved into 

 water and carbonic acid by the combined effect of light and free 

 oxygen, and a typical representative of the diastases, the invertive 

 ferment of cane-sugar, had its qualities completely destroyed by sun- 

 light, which was, however, without effect in a vacuum or a neutral 

 atmosphere. During the past eight years evidence confirmatory of 

 these conclusions has accumulated from various sources, and the 

 principal facts are reviewed by the author. 



After referring to the observations of Warington and others on 

 the nitrifying ferment, of Tyndall in regard to the insolation of 

 putrefiable infusions under an Alpine sun, and to others, Dr. Downes 

 summarizes the recent results of Duclaux,* who finds, from an ex- 

 amination of several species, that Micrococci are apparently far more 

 sensitive to sunlight than the more resistant spore-forming Bacilli. 

 Duclaux, who has likewise observed the destructive effect of sunlight 

 on a diastase, agrees that this injurious action on germs is an affair of 

 oxidation. In his previous papers the author had noted the different 

 powers of resistance of various organisms to sunlight, notably of 

 Saccliaromycetes or Mucedines, as compared with Bacteria. He now 

 describes a specially resistant Bacterium, roughly resembling, but not 

 identical with, the Ascohacterium of Van Tieghem, of which he finds 

 no previous record. 



In refuting the conclusion of Jamieson, an Australian observer, 

 that both he and Prof. Tyndall had mistaken effects of heat for effects 

 of radiant energy distinct from heat. Dr. Downes describes recent ex- 

 periments of his own, which indicate that a similar action, though of 

 course in a less degree, is exercised by diffused light. He concludes 

 with a reference to the well-known observations of Pringsheim on the 

 destruction of vegetable protoplasm by the more refrangible rays, and 

 claims them as evidence of the truth of his former generalization, 

 that the hyper-oxidation of protoplasm by light is a general law, from 

 the action of which living organisms require to be shielded by a 

 variety of protective developments of cell-wall, aggregation of tissue 

 or colouring matter, and in other ways. 



* See this Journal, v. (1885) p. 1047. 



