Journal of Applied Microscopy. 



211 



added to bring the total volume of the 

 liquids to the shoulder of the test 

 bottles; the milk and acid are then mixed 

 thoroughly, and when a homogeneous 

 dark mixture has been obtained, more 

 acid is added until the liquid reaches the 

 top of the scale on the neck of the bottles. 

 The contents are again mixed by invert- 

 ing the bottles a couple of times, keeping 

 the mouths of the bottles tightly closed by 

 pressing over them a small piece of sheet 

 rubber. The bottles are then whirled for 

 one to two minutes, and readings taken 

 at once. If the contents have contracted 

 by cooling during the centrlfuging, so 

 that the fat column is below the gradu- 

 ated scale, the bottles are placed in hot 

 water for a few minutes prior to reading 

 off the results. Instead of using concen- 

 trated sulphuric acid, the commercial 

 acid (specific gravity, 1.82-1.83) may be 

 used, provided the milk-acid mixture be 

 kept in water of about 200 degrees F. for 

 a few minutes before the bottles ai'e 

 whirled. The ordinary time of four min- 

 utes for whirling the best bottles in the 

 Babcock test may be reduced to less than 

 two minutes with the urinary centrifuge, 

 owing to the high speed reached in this 

 machine. 



On account of the small quantity of 

 milk that can be handled it is but nat- 

 ural that the determination of fat in milk 

 by means of this centrifuge requires some 

 nicety of manipulation not called for 

 when the test is made with regular Bab- 

 cock test bottles and test machines, when 

 nearly nine times as much milk is taken. 

 After a little practice there will, how- 

 ever, be no difflculty in obtaining accu- 

 rate and satisfactory results with the 

 small centrifuge and bottles, and 

 this may also in this respect prove a 

 valuable adjunct to any pathological or 

 physiological laboratory where analyses 

 of human or cow's milk are occasionally 

 called for. The practitioner will likewise 

 find it useful in making analyses of such 

 milk in the study of special cases and for 

 hygienic-economical examinations. 



The interested reader will find a full 

 discussion of the Babcock test and of the 

 general subject of milk analysis in a 

 work recently published by Professor E. 

 H. Farrington, of this university, in con- 

 junction with the writer.tt 



ttTestlng Milk and its Products, Mendota 

 Book Co., Madison, Wis., Fourth Edition, 

 1899. 



F. W. WoiL. 

 Chemist to Wisconsin Agricultural Ex- 

 periment Station, Madison, Wis., De- 

 cember, 1898. 



Mr. Charles J. Chamberlain will begin 

 a series of articles on Botanical Micro- 

 technique in an early number of the 

 1899 Journal. 



Laboratory Methods in Bacteriol- 

 ogy. 



Dr. F. G. Now. 



IV. — The Staining of Bacteria in Sections- 



In order to ascertain the presence and 

 especially the distribution of bacteria 

 within the tissues and organs, it is neces- 

 sary that small portions of the latter be 

 hardened, then cut into sections and 

 stained by appropriate methods. 



As a rule, the tissue to be hardened 

 should be cut up into small pieces, which 

 should not be more than a quarter of an 

 inch in thickness. It is always advisable 

 to place the pieces of tissue on a piece 

 of filter paper, or on some absorbent cot- 

 ton. The liquid thus has free access to 

 all parts of the tissue. The fixing and 

 hardening of tissue which is to be stained 

 for bacteria is usually done in alcohol, 

 mercuric chloride, or in a formaldehyde 

 solution. The details for fixing and hard- 

 ening of tissues have been clearly stated 

 by Dr. Huber in the March number of 

 the Journal, and for that reason will be 

 omitted in this connection. 



It will be seen that, no matter what 

 solution is used for fixing, eventually the 

 tissues are placed in absolute alcohol. 

 When thoroughly dehydrated, the 

 material is now ready for cutting direct 

 or for imbedding and subsequent cutting. 

 The alcohol-hardened tissue may be cut 

 direct, or may be softened by soaking 

 in water and then frozen and sectioned. 

 It is preferable, however, to imbed the 

 tissue in paraffin or in celloidin, in which 

 case thinner and better sections may be 

 obtained. 



The paraffin method is easy of execu- 

 tion and is to be recommended for the 

 preparation of sections which are to be 

 stained for bacteria. 



Inasmuch as Dr. Huber has given 

 extended and explicit directions for im- 

 bedding in paraffin, the reader will do 

 well to refer to his paper in the April 

 number of this journal (page 70). The 

 material, once imbedded in paraffin, may 

 be preserved in this condition indefinitely. 

 Many bacteria, especially the leprosy and 

 tubercle bacilli, lose their characteristic 

 staining properties when the tissues 

 which contain these organisms are pre- 

 served in alcohol. This can be obviated 

 by keeping the material in paraffin. 



The details for cutting paraffin sec- 

 tions and for affixing these on cover- 

 slips are also given in Dr. Huber's papers 

 (pp. 85, 103). After the removal of the 

 paraffin from the sections, by means of 

 xylol, they are ready to be stained. 



The beginner will do well to stain sec- 

 tions of the kidney, liver, lungs, or spleen 

 of a rabbit or guinea-pig which has died 

 of anthrax. This material will serve ta 



