EXPLANATION OF PLATE V. 



Fig. 41. Effect of the cover-glass on the rays from the object to the objective 

 (Ross). 



Axis. The projection of the optic axis of tbe microscope. 

 F. Focus or axial point of the objective. 



F / and F". Points on the axis where rays 2 and 3 appear to originate if traced 

 backward after emerging from the upper side of the cover-glass (cover). 



It is for the correction of this disturbance or so-called "negative aberration" 

 produced by the cover-glass that objectives are fixed in their mounting for a given 

 thickness of cover, or that the combinations making up the objective are made 

 adjustable ; that is so that the back combinations may be brought nearer the front 

 lens or combination as the cover thickens, and separated with a thinner cover or 

 for uncovered objects. The thicker the cover, the nearer the front and back com- 

 binations ; the thinner the cover the farther apart are front and back placed (§ 63). 

 Fig. 42. Showing the course of the rays passing through a cover-glass from an 

 axial point of the object, and the number that finallv enter the front of a dry ob- 

 jective. 



Fig. 43. Rays from the axial point of the object traversing a cover of the same 

 thickness as in Fig. 42, and entering the front lens of a water immersion objective. 

 Fig. 44. Rays from an axial point of the object traversing a cover-glass and en- 

 tering the front of a homogeneous immersion objective. 



Figures 42-44, are somewhat modified from Ellenberger, and are introduced to 

 illustrate the relative amount of utilized light, with dry, water immersion and 

 homogeneous immersion objectives (§§ 9, 10, 18). 



Fig. 45. Absorption Spectrum of Oxy-Hsemoglobin or arterial blood (1) and of 

 Haemoglobin or venous blood (2). (From Gamgee and MacMunn.) 



A, B, C, I), E, F, G, H. .Some of the principal Fraunhofer lines of the solar 

 spect. nm (i< 129). 



.90, .80, .70, .60, .50, .40. Wave lengths in microns, as shown in Angstrom's 

 scale (§ 138). It will be seen that the wavelengths increase toward the red and de- 

 crease toward the violet end of the spectrum. 



Red, Orange, Yellow, etc. Color regions of the spectrum. Indigo should come 

 between the blue and the violet to complete the seven colors usually given. It 

 was omitted through inadvertence. 



Fig. 46. Centering card to enable one easily to put objects in the center of a 



slide. It is made by drawing concentric circles in the center of a card and pasting 



pieces of board, or card board in the proper position to serve as guides to the slide. 



Fig. 47. -Small spirit lamp modified into a balsam bottle or a glycerin or glycerin- 



jellv bottle. By adding a small brush, it answers well for a shellac bottle also. 



Fig. 48. Pipette for delivering drops or a small stream of any liquid. Made by 

 tying sheet rubber over the top of a thistle bulb and connecting the bulb with a 

 tapering "lass tube by a piece of rubber tube. 



Fig. 49. Glass slide with cover-glass, a drop of reagent and a bit of absorbent 

 paper to show method of irrigation ($ 197). 



Fig. 50. Slide and cover- glass showing method of anchoring a cover-glass with a 

 glvcerin preparation when no cell is used. A cover-glass so anchored is not liable 

 to move when the cover is being sealed {\ 169). 



Fig. 52-56. Various apparatus for the preparation of fibrin and for counting 

 blood corpuscles, milk globules, etc. (These figures belong to Part II). 



