126 APPENDIX. 



In Milk. — It forms a floating black crust, with a dusky grey tint on 

 its upper surface. The milk itself becomes of a muddy colour from 

 an invasion of the deeper layers by colonies of the organism. 



Microscopically. — Like Fink Torula, but with a dark brown pigment. 



Mycoderma aceti. In Grape Jicice. — The vinegar plant appears 

 as a floating film, which rapidly covers the whole of the surface of the 

 liquid. It is a typical aerobe, and cannot live in the lower strata of 

 the liquid. This necessity of oxygen permits of its exclusion from 

 beer vats, the empty air space at the surface being in this case filled 

 with carbonic acid gas, which inhibits the growth of the plant. The 

 film is either corrugated to a very great extent, or it may be quite 

 smooth, depending on the exact species present. 



Microscopically. — The film is found to consist of immense aggrega- 

 tions of elliptical or cylindrical cells 6 n. long by 2 or 3 //.. broad, 

 arranged in irregular branching chains. Multiplication, as in the 

 Torulce proper, by buds and by spores, which appear in the central 

 portions of the cell contents. 



M. aceti will also grow feebly on hay infusion, but not on the 

 animal infusions. 



Sarcina. In Milk. — Causes a dense coagulum, which sinks in 

 irregular masses to the bottom of the whey, which replaces the 

 sterile milk. 



Microscopically. — Three species are recognised : — 



S. ventriculi. — Round cells in clusters of four or multiples of four. 



Cells about 4 /i. in diameter, with cell contents frequently 



pigmented yellow or light brown. 



In the stomach they do not form such large aggregations as 



in artificial media (e.g., milk), the layer colonies being pro- 

 bably broken up by mechanical unrest. 

 S. urina. — Cells very small, i /*. diameter, mode of growth and 



reaction in milk similar to those of S. ventriculi. Found in 



fresh urine. 

 S. hyalina. — Round cells, 2 /x. diameter, forming clusters which 



lie in a hyaUne matrix. Found in ditch water. 



BACTERIDS. 



Short cylindrical freely moveable cells, with or without flagella ; in 

 some cases alternating with an intermediate stage, in which the im- 

 mobile organisms are collected together into zooglea masses. 



Bacterium termo. On Potato. — It forms a dusky grey glutinous 

 layer, covering rapidly the whole of the cut surface. At the edges, 

 where the process of multiplication is most rapid, the film has a cor- 

 rugated appearance. 



