Sellers.] lbO [March 21, 



D. S. IIOLMAN'S DEVICE FOR THE MICROSCOPIC 

 EXAMINATION OF FLUIDS. 



By W. Coleman Selleks. 

 {Bead before the American Philosophical Society, March 21, 1873.) 

 In a slip of plate glass 1" wide, 3" long, £ in. thick, two circular con- 

 cave cells are ground, there being a space of T V in. left between the cells. 

 These cells, which are about ^ in. in diameter and as deep as the glass 

 will permit— say j\ in. deep — are united by a very shallow channel some- 

 what below the centre of the two cells, so that with cells placed y 1 ^ in. 

 apart, the channel is about fV in. long. Both the cells and channel are 

 polished. If a few drops of blood be placed in these cells, and a cover of 

 thin -lass be pressed down, some of the blood, finding its way between 

 the surfaces in contact, will dry, and act as a cement to hold the fluid 

 blood in the cells in place. The quantity of blood being insufficient to fill 

 the cells, a considerable amount of air becomes imprisoned with the blood, 

 and the expansion of the air in either cell will drive the blood through the 

 channel into the adjacent cell, and in the shallow channel it is presented 

 under the most favorable condition for examination. By holding the top 



of the finger near one or the other cell, the heat is enough to cause the 

 expansion and a consequent more or less rapid flow of the fluid through 

 the channel. This flow may be arrested or continued and reversed at 

 will by change of position of the finger, so that any particles floating in 

 .in the fluid can pass in succession across the field, but can be arrested 

 and examined with ease at will. 



Blood or other fluid inclosed in the cells remains in good condition for 

 examination for several days, and changes undergoing in the fluid can be 

 examined. 



Mr. Hoiman exhibited the slide containing human blood, and showed 

 the white corpuscles like the amebae found in water, and called attention 

 to the change in form of these minute bodies, similar in every way to 

 the amoeboid action noticed in the forms found in water, i. e., a change 

 of form, jutting out projections of its body, and consequent entire change 

 of form of the entire body, and by such change, a kind of slow locomo- 

 tion. Within these amceba-like forms were plainly seen certain minute 

 specks, which had a motion among themselves similar to the so-called 

 molecular motion. Mr. Hoiman thought it barely possible that these 



