824 SUMMARY OK CURRENT RESEARCHES RELATING TO 



(6) Miscellaneous. 



Preserving Brains.* — A. Starcke suspends brains in 15 p.c. forma lit, 

 for 8 to 1 I days. On removal the surface is carefully dried ; it is then 

 immersed, vertex downwards, in a vessel filled with hard paraffin, heated 

 to at least 15° above its melting-point ; a quick turn covers the surfa<< 

 with a mantle of paraffin. Should any gaps be found, the places im- 

 plicated must be treated anew. Brains treated in this manner will, 

 even after five years, give satisfactory preparations by Xissl's or Weigert's 

 methods of staining. 



Turbidometer for Counting Vaccines. f—C. F. Pawson and H. P. 

 Bassett have devised an apparatus for estimating the number of bacteria 

 contained in a certain volume of an autogenous vaccine. To the 

 sliding bar of the mechanical stage of a Microscope is fixed a vertical 

 rod — a hypodermic needle will serve — which dips into a rectangular 

 glass box, fixed to the table. At one end of the box is a transparent 

 circle which admits light ; the other end is attached to a cylindrical 

 metal tube, leading to a semicircular eye-shield, at the edge of the 

 table. This shield screens the observer. If the box be filled with 

 a turbid liquid, and the vertical rod be observed through the tube, 

 as it is moved from the proximal towards the distal end of the box, a 

 point is reached where, owing to the opacity of the intervening 

 fluid, it disappears from view. The point at which this takes place 

 depends upon the degree of turbidity. As this only gives a relative 

 observation, it is necessary to have a standard. McFarland has devised 

 a series of test-tubes containing different amounts of freshly precipitated 

 barium sulphate. Tube No. 5 of his series contains sufficient precipi- 

 tate to produce turbidity equal to that of a suspension of fifty million 

 bacteria per cubic centimetre. This is taken as the standard. The 

 vertical rod is moved to the proximal end of the box, and a reading 

 taken from the scale on the mechanical stage. The box is filled with 

 standard suspension, and the rod is made to move until it can no longer 

 be seen. A second reading is taken. The difference between these 

 readings gives the amount of translation of the rod. Similar observa- 

 tions are taken with the vaccine which is under investigation. The 

 excursions of the vertical rod are inversely proportional to the turbidity 

 of the samples ; and so from these data, an estimate may be formed of 

 the strength of the bacterial emulsion. 



Agglutination of Trypanosomes.J — Lange describes a method by 

 which a macroscopic agglutination test for trypanosomiasis may be carried 

 out. For this purpose the author makes use of a suspension of trypano- 

 somes obtained from the blood of a highly-infected animal. The blood 

 is lightly centrifugalized, so that the organisms settle into a definite layer, 

 which is then removed by means of a pipette. This emulsion is then 

 washed in salt solution, centrifugalized and suspended in a fresh quantity 

 of salt solution. A small quantity of formalin is added, and the suspen- 



* Zeitschr. wiss. Mikrosk., xxviii. (1911) pp. 150-1. 



+ Centralbl. Bakt., lte Abt. Orig., lviii. (1911) pp. 638-40. 



: Centralbl. Bakt., lte Abt. Ref., i. (1911) Beib. pp. 171-7. 



