222 AIDS TO BACTERIOLOGY 



apparatus used in haematological work. This method seems 

 to allow a closer approach to accuracy than most others. 

 Houston, in his report to the L.C.C., dilutes the ' filth ' 

 obtained by his apparatus, and makes definite-sized 

 cover-glass preparations with 0*01 c.c. of the sediment. 

 The number of cells found in the sediment bears no con- 

 stant proportion to the total number present in the milk 

 (Breed). 



Examination of Sediment. The strippings, or milk last 

 drawn, is the best for examination purposes (Mettam). 

 The milk is centrifuged for twenty minutes at 1,500 revo- 

 lutions per minute. At about half-time, the centrifuge 

 is stopped and the cream stirred up in the upper part of 

 the milk. This disentangles a good many organisms, 

 cells, and other matter, that have been lilted up by the 

 fat globules. The centrifuging is completed, and the fat 

 and liquid tipped out. Three slide preparations are made, 

 each with four drops of the sediment, which are spread 

 evenly over three-fourths of the slide. The slides are 

 air-dried, and then treated with a mixture of absolute 

 alcohol and ether for ten minutes. One slide is stained 

 with Loftier' s blue, another by Gram's method, and a 

 third by the Ziehl-Neelsen method. The L6 flier's blue, 

 specimen gives a general idea of the number and kinds 

 of bacteria and cells present. The number of leucocytes 

 in twenty fields should be counted, and if they average 

 more than twenty per field (with a j 1 ., inch), it is pretty 

 certain that pus is present. This is confirmed if in this 

 and the Gram specimens large numbers of streptococci 

 of the longus type are found. Confirmatory evidence is 

 obtained if in a fresh specimen (undried) of the sediment 

 mounted in a drop of Gram's iodine solution red blood- 

 cells are seen in addition. The sediment should also be 

 examined fresh with the low powers ( and ^ inch) for 

 gross and filth contaminations e.g., hair, straw, sand, 

 vegetable matter, etc. 



The slide stained by the Ziehl-Neelsen method should, 

 after treatment with acid, be treated with alcohol 

 (p. 74) to decolorise any smegma bacilli, which are some- 

 times found in milk. Unless tubercle bacilli are found 

 before, this slide should be searched for at least half an 

 hour. It must be noted that milk may contain such 

 acid-fast saprophytes as the Timothy-grass bacillus, and, 



