280 



BLOOD AND BLOOD EXAMINATION 



mits the sunlight to penetrate this for a definite time. The degree of black- 

 ening which the paper shows under the blood layer is compared with a stand- 

 ard scale, and then the hemoglobin is read from a table which has been obtained 

 empirically. 



In quite a series of investigations I have compared 

 the results obtained with the apparatus of Gowers and 

 Gaertner and have found reasonable uniformity. 



Fig. 12. — Hemophotogeaph. (After Gaertner.) 



' =^>m 



Fig. 13. — Hemophotograph. 

 (After Gaertner.) 



When by the aid of some of these instruments a result has been obtained, 

 it must always be borne in mind that no exact test has been made, that, on the 

 contrary, all sorts of errors may be present. Those which are due to the 

 imperfections of the instrument I have already pointed out; and we must 

 always assume 5 to 10 per cent, of errors in the examination of a definite drop 

 of blood, even although we are quite expert in the examination; with the 

 novice this percentage may be much greater. Unfortunately, it is impos- 

 sible by the use of more exact so-called physiologic methods to avoid these 

 errors in the estimation of hemoglobin, partly because the methods are com- 

 plicated, and partly because they require too large amounts of blood, and, 

 therefore, cannot be utilized in practice. 



To these errors, which are, however, due to the methods or instruments, 

 still others must be added which are due to a certain changeability in the 

 blood itself. It is well known that the most varied influences may change 

 the caliber of the blood-vessels, by stimulating the vaso-dilators or the vaso- 

 constrictors ; for example, light, heat, cold, muscular activity, etc. Accord- 

 ing to the caliber of the vessels — of course within certain narrow limits — 

 the number of corpuscles in the capillary blood will vary, and with this the 

 amount of hemoglobin, the specific gravity, the total solids and the albumin 

 contents of the blood. Moreover, if the blood to be examined is not obtained 

 by puncture or incision of the blood-vessel directly, but, as in the great major- 

 ity of cases, by a prick in the finger or by wet cups, the unavoidable admixture 



