STIMULI AND THEIR ACTIONS 431 



stronger, an extension of the infection throughout the organism takes 

 place, and the course of the disease is then determined by other 

 factors. 



In order to demonstrate the positively chemotactic action of 

 bacterial products upon leucocytes, the following experiment of 

 Massart can be performed. According to a method first devised 

 by Pfeffer, a short capillary tube is filled with a culture of the pus- 

 forming Siaphylococciis pyogenes albus, and one end is sealed, The 

 tube is laid in the abdominal cavity or under the skin of a rabbit, 

 and left for some 10 to 12 hours. After this time it is found by 

 microscopic examination of the tube that through the open end a 

 dense swarm of leucocytes has penetrated into the interior, and 

 has closed the opening like a thick white stopper (Fig. 208). In 

 other words, the leucocytes are induced by the bacterial substances 

 to creep from the tissues of the animal into the capillary tube. A 

 critic will at once raise the objection that perhaps it is the 

 nutrient solution in which the bacteria are cultivated, which 

 acts chemotactically upon the leucocytes. This objection can be 

 nullified, if, as Massart has done, there be put into the animal for 



FIG. 208. Chemotaxis of leucocytes toward pus-cocci. The leucocytes have wandered in dense 

 crowds into u capillary tube, which contains a culture of Slaphylococcus ', they may be seen 

 especially at the opening of the tube. 



purposes of control a similar capillary tube containing similar 

 nutrient liquid but without the bacterial culture. In such a case 

 the leucocytes do not enter. That it is not simply the bodies of 

 the bacteria themselves, but the metabolic products excreted by 

 them, which have the chemotactic effect, may be proved by employing 

 for the experiment a culture liquid that has been sterilised and 

 wholly freed from the bacterial bodies, and in which, therefore, 

 only the dissolved metabolic products of the bacteria in question 

 exist. The result is then the same as when the culture is employed 

 directly : after some time the tube is filled with leucocytes that 

 have wandered in. What is true of the culture of Staphylococcus 

 pyogenes albus has been found also in many other pathogenic 

 Bacteria, and there is no doubt that further investigations upon 

 the relations between leucocytes and bacteria will make clear 

 a whole series of points which thus far in the history of infectious 

 diseases have been very obscure. 



Moreover, leucocytes appear chemotactic, not only toward the 

 metabolic products of Bacteria, but also, as Buchner has found, 

 ttoward the proteids of the bodies of the Bacteria themselves, and 



