276 BLOOD AND BLOOD EXAMINATION 



certain infectious diseases protective bodies may be demonstrated in the blood 

 serum. 



After these brief indications it will be seen that we have quite a large field 

 of activity, even if we limit ourselves to such an investigation of the blood 

 as is of immediate clinical importance. It is impossible, however, to omit a 

 brief explanation of the normal physiology and anatomy of the blood, as this 

 enables us to measure the degree of pathological change liable to occur. 



We must first decide upon the best method of obtaining the amount of 

 blood necessary for investigation. Of course for clinical purposes only those 

 methods of examination are valuable which need no more than one or two 

 c.c, or — if there be a necessity for frequent repetition — a few drops of blood.' 

 Consequently, many clinical methods, compared with strict physiological 

 processes, sufEer more or less in reliability. This fact has lately given rise to 

 an endeavor to modify certain physiological methods which hitherto have 

 necessitated large quantities of blood. The results have, in the main, been 

 rather unsatisfactory. This is true, for example, of the "clinical" estima- 

 tion of the alkalinity of the blood, and of the iron and phosphorus in the blood. 

 If large quantities of blood cannot be obtained, it is better to refrain entirely 

 from such estimations than, by an appearance of exactness, to produce figures 

 of questionable value. 



Fortunately, however, for many important clinical investigations, only a 

 few drops of blood are necessary, and these are best obtained under aseptic 

 precautions by a simple prick of the finger, of the toe, or of the lobe of the ear. 

 [In America the finger is rarely used, as the pain of puncture is much greater 

 than in the ear. An ordinary glover's needle (bayonet-pointed) is convenient, 

 cheap and efficient. A sewing needle can be used but does not answer nearly 

 as well. — Ed.] By friction or by active muscular movement these portions of 

 the body may previously be made somewhat hyperemic. In general the choice 

 of the place is immaterial; for smear preparations the finger is preferred. 

 In very sensitive patients, provided the investigation is to be repeated fre- 

 quently, the ear is chosen. The prick is made with half of a steel pen or with 

 a Soennecken's lancet; but we may also use the so-called "pistol knife" in 

 which the needle-shaped knife may be adjusted, and, by pressure of the spring, 

 inserted to an exact depth. 



If larger quantities of blood, i. e., a few cubic centimeters or more, are 

 necessary it is advisable, provided there is no contra-indication, to obtain the 

 material by wet cups ; in which proceeding it must of course be remembered 

 that blood thus obtained is more or less admixed with lymph. Finally punc- 

 ture of a dilated vein of the arm by the aid of a Pravaz syringe, which is very 

 readily performed, or an ordinary venesection may be resorted to. 



The withdrawal of blood, if performed aseptically, is entirely without dan- 

 ger and, as a rule, does not disturb the patient in the least. We should never 

 forget, before proceeding, to assure ourselves that we are not dealing with a 

 hemophilic. In such persons, even with a simple puncture of the finger, there 

 may be great difficulty in stopping the flow of blood. [In such cases a mere 

 touch of the needle point to the skin will give us all the blood needed without 

 producing any troublesome hemorrhage. — Ed. J 



