840 REPORT— 1897. 



observers Downes and Blunt showed long ago that if bacteria in a nutrient liquid 

 are exposed to sunlight, they are rapidly killed. Further researches, in which I 

 have had some part, gradually brought out the facts that it is really the light rays 

 and not high temperatures which exert this bactericidal action, and by means of a 

 powerful spectrum and apparatus furnished by the kindness of Professor Oliver 

 Lodge I was able to obtain conclusive proof that it is especially the blue-violet 

 and ultra-violet rays which are most efiective. This proof depended on the pro- 

 duction of actual photographs in bacteria of the spectrum itself. Apart from this, 

 I had also demonstrated that just such spores as those of anthrax, at the same 

 tim3 pathogenic and highly resistant to heat, succumb readily to the action of 

 these cold light-rays, and that under conditions which preclude their being poisoned 

 by a liquid bathing them. 



The work of Brown and Morris ou the daily variations of diastatic enzyme in 

 living leaves, and especially Green's recent work on the destructive action of light 

 on this enzyme, point to the probability that it is the destruction of the enzymes 

 with which the bacterial cells abound which brings about the death of the cell. 



That these matters are of importance in limiting the life of bacteria in- our 

 streets and rivers, and that the sun is our most powerful scavenger, has been 

 shown by others as well as myself. In this connection may also be mentioned 

 Martinand's observations, that the yeasts necessary for wine-making are deficient 

 in numbers and power on grapes exposed to intense light, and he explains the 

 better results in Central France as contrasted with those in the South as largely 

 due to this fact. Whether, or how far, the curious effects of too intense illumina- 

 tion in high latitudes and altitudes on plants which might be expected to grow 

 normally there, can be explained by a destructive light action on the enzyme of 

 the leaves, has not, so far as I know, been tested ; but Green's experiments 

 certainly seem to me to point to the possibility of this, as do the previous 

 experiments with screens of Pick, Johow, myself, and others. 



It is interesting to note that "Wittlin and others have confirmed the conclusion 

 my own few trials with Eijntgen rays led to ; they show no action whatever. 



That branch of mycology which is now looked upon by so many as a separate 

 department of science, usually termed bacteriology, only took shape in the years 

 1875-79, when its founder, the veteran botanist Cohn, who recognised that the 

 protoplasm of plants corresponded to the animal sarcode, and who has been 

 recently honoured by our Royal Society, published his exact studies of these 

 minute organisms, and prepared the way for the specialists who followed. 



It is quite true that isolated studies and observations on bacteria had been 

 made from time to time by earlier workers than Cohn, though it is usually over- 

 looked that Cohn's first paper on Bacteria was published in 1853. Ehrenberg 

 in particular had paid special attention to some forms ; but neither he nor his 

 successors can be regarded as having founded a school as Cohn did, and this 

 botanist may fitly be looked upon as the father of bacteriology, the branch of 

 mycology which has since obtained so much diversity. 



It should not be overlooked that the first proof that a specific disease of the 

 higher animals is due to a bacillus, contained in Koch's paper on Anthrax, was 

 published under Cohn's auspices and in his ' Beitriige zur Biologic der Pflanzen ' 

 in 1876, four years after Schroeter's work from the same laboratory on pigmented 

 bacteria, and that the plate illustrating Koch's paper was in part drawn by Cohn. 



It is of primary importance to recognise this detail of Koch's training under 

 Cohn, because, as I have shown at length elsewhere, popular misapprehensions as 

 to what bacteriology really consists in have been due to the gradual specialisation 

 into three or four ditlerent schools or camps of a study which is primarily a branch 

 of botany ; and, again, it is of importance to observe that the whole of this particular 

 branch of mycology, to which special laboratories and an enormous literature are 

 now devoted, has arisen during the last quarter of a century, and subsequent to 

 the foundation of scientific mycology by De Bary. When we reflect that the 

 nature of parasitic fungi, the actual demonstration of infection by a fimgua spore, 

 The tra^nsmis.sion of germs bv water and air, the meaning and significance of poly- 

 morphism, heteroecism, synbiosis. had already been rendered clear in the case of 



