16 EXPERIMENT STATION RECORD. 



mo.vdy (Ann.Phys., 4-ser., 10 {190-3) , No. 1, pp. 1-39, figs. 13). — A method of so light- 

 ing objects that those ordinarily invisible under the microscope are rendered visible 

 is described, which is similar in principle to the commonly observed fact that a beam 

 of sunlight in a darkened room renders moats visible. 



Light was collected and allowed to strike on the material to be examined at right 

 angles to the line of vision through the microscope. It was found that materials 

 were rendered visible which were in size somewhere between molecular dimensions 

 and the length of a light wave. The minute particles rendered visible had in general 

 a brilliant appearance. The accuracy of the method, its theoretical limitations — that 

 is, the size of the smallest particles which can theoretically be rendered visible — as 

 well as related topics, are discussed and results of a number of experiments with 

 glass colored with gold are reported. 



The author points out that the method is capable of application to the examina- 

 tion of colloid substances and similar bodies, and there is no theoretical reason why 

 large complex molecules such as occur with proteids, potato starch, etc., should not 

 be rendered visible. 



TJltramicroscopic investigations, Much, Romeb, and Siebekt (Ztschr. Diaiet. u. 

 Phys. Ther., 8 (1904), Nos. l,pp. 19-27; 2, pp. 94-96) .—Using the method and appa- 

 ratus devised by Siedentopf and Zsigmondy (see above), the authors studied 

 especially the proteid bodies in a number of substances, including horse serum, milk, 

 milk serum, mucin solution, etc. 



It was found that when the method was applied to proteid solutions glittering 

 moving particles were observed, which varied in number with the concentration of 

 the solution. These particles were regarded as the protein molecules or molecular 

 groups. The authors devised a method of studying the proteid solutions quantita- 

 tively, which depended on diluting the solution to such an extent that only three or 

 four of the glittering particles were observed in the field of vision. The amount of 

 dilution is called the "ultra value." This varied in substances examined from 250 

 with Marburg nutrient bouillon to 800,000 with milk serum. 



A number of samples of urine were examined, and it was found that the method 

 was especially satisfactory for the detection of albumen, and in the authors' opinion 

 is as valuable for the quantitative determination of albumen as is the polarization 

 apparatus for the determination of sugar. 



Some of the experiments reported had to do with the products of digestion. It 

 was found that when 0.5 gm. of globulin from horse-blood serum was mixed with 

 0.5 gm. pepsin and 0.2 gm. hydrochloric acid, and diluted to 100 cc, that the ultra 

 value was 100,000. After standing for half an hour in the incubating closet the ultra 

 value was 100, and after one hour and a half, 25. When milk was digested with 

 pepsin and hydrochloric acid no diminution in the number of particles was notice- 

 able. This was also the case when digested with pancreatin, but if the pancreatin 

 digestion followed that with pepsin and hydrochloric acid the number of particles 

 diminished. 



Twenty cubic centimeters of fat-free milk diluted with distilled Mater to 100 cc. 

 had an ultra value of 750,000, and showed large particles and particles which were 

 smaller and less glittering. Treated with 0.1 gm. pepsin and 0.4 gm. of 25 per cent 

 hydrochloric acid, this quantity of fat-free milk had an ultra value of 500,000 after 

 standing in the incubating closet 2 hours, and an ultra value of 750,000 after 

 standing 24 hours. This remarkable increase in the number of visible particles was 

 confirmed by control experiments. After standing 62 hours the value decreased to 

 250,000, and none of the large light particles were observed. 



Tests were also reported with whey (lacto serum), which the authors consider of 

 especial interest on account of the bactericidal properties. The conclusion was 

 reached that the bactericidal and agglutinating properties go hand in hand with the 

 number of particles rendered visible by the "ultra apparatus." In these tests and 



