746 EEPORT — 1887. 



different places lias been called attention to, and the metbods of experiment fully 

 described. As these investigations were carried out with the aid of solid nourish- 

 ing media, we were able to obtain a collection of piu'e cidtivatious of a number of 

 micro-organisms derived directly from the air. It is not unnatural that the brilliant 

 discoveries in connection with the etiology of infectious diseases should have ab- 

 sorbed the lion's share of the attentioii of investigators in the iield of bacteriology, 

 and that the non-pathogenic organisms should have come to be regarded as 

 comparativeh' uninteresting by the side of their more formidable brethren. But 

 the conversion of sugar into alcohol, the decomposition of nitrogenous organic 

 matter with elimination of ammonia, the oxidation of ammonia to nitrous and 

 nitric acids, besides many other natural transformations which are effected through 

 the agency of such micro-organisms, are certainly not second in importance to the 

 results, terrible as they often are, achieved by the pathogenic forms. The organisms 

 producing the above-mentioned changes are known to be present in the air, and 

 there can be little doubt that the numerous other aerial varieties wiU in the future 

 be found to discharge important duties in the laboratory of Nature. 



We have provisionally given names to the various forms, by which we have 

 endeavoured to indicate some striking peculiarity which the organisms present when 

 examined either in their cultivations or under the microscope. 



(1) Micrococcus carnicolor. — This is a micrococcus which, when microscopically 

 examined imder a high power ( x 1000), is seen to consist of almost round cocci, 

 varying in size from '5 /x to about I'S /n. The larger forms almost invariably exhibit 

 a division. It produces on gelatine-peptone a flesh-coloured expansion, and only 

 liquefies the gelatine in very old cultivations. On agar-agar it grows rapidly, pro- 

 ducing the same characteristic shining flesh-coloured expansion. In broth the 

 liquid is clear, free from pellicle, and has a pinkish deposit at tlie bottom of the 

 tube. When plate-cultivated, the colonies to which it gives rise are seeu to be of 

 a faint pink colour. Under the microscope those in the depth are almost perfectly 

 circular and smooth-edged, whilst on the surface they form a thin, almost colourlesa 

 expansion, which, later, acquires the characteristic pink tint. 



(2) Micrococcus (tl!/us. — This is seen under a high power to consist of cocci 

 varying in size from -S/i to l"5/i, the larger ones presenting a division. On gela- 

 tine-peptone it produces a white shining expansion, with a lobular and smooth edge. 

 It does not liquefy the gelatine. On agar-agar it forms a faintly white, almost 

 colourless, surface-expansion. In broth it renders it very slightly turbid, produces 

 no pellicle, and forms a yellowish-white deposit. The colonies look like small milk- 

 white discs, and under the microscope appear circular and with a sharp edge. 



(3) Streptococcus liquefaciens. — This is a small micrococcus, varying in size 

 from '5 fx to '8 jx, which hang together in short chains. It liquefies the gelatine 

 slowly, producing a light lemon-yellow deposit. On agar-agar it grows slowly, 

 producing an almost colourless shining expansion. In broth it produces a dirty 

 yellowish-white deposit, the liquid remaining clear and free from peUicle. The 

 colonies appear as yellowish pin-heads on the surface, each being surrounded by a 

 slight depression. Under the microscope they are seen to be not always circular, 

 but the edge is smooth. 



(4) Sarcina lutea. — Under a high power there are seen large cocci mostly 

 grouped together in cubical packets of four or more. It is best seen when lightly 

 stained with methylene-blue. On gelatine it produces a strong lemon-yellow pig- 

 ment, and causes very slow liquefaction of the medium. On agar-agar this cha- 

 racteristic lemon-yellow pigment is again produced. In broth the liquid is clear 

 and free from peUicle, but it has formed a lemon-yellow deposit. The colonies 

 appear as small yellow centres, whilst under the microscope they are seen to be 

 irregular in shape with a nearly smooth edge. 



(o) Sarcina aurantiaca. — The packets which this organism forms are seen to be 

 much smaller than those of Sarcina lutea. It liquefies the gelatine and forms a 

 flocculent orange deposit. On agar-agar it grows rapidly, producing a strong orange 

 pigment. In broth it renders the liquid turbid and forms an orange deposit. The 

 colonies appear as small, round, yellow dots, which exhibit a circular depression. 

 Under the microscope they are seen to be circular, with a slightly denticulated edge. 



