Part XIL 
SUMMARY AND CONCLUSIONS. 
Profound chemical changes, perhaps in the central nervous S3"stem, 
are probably produced hj the first injection of a strange proteid. 
Guinea pig's may be sensitized with horse serum bj- injections 
directl}" into the heart. From this it appears that the cells lining the 
peritoneal cavipy or the connective tissue cells of the subcutaneous 
tissue do not necessarily play a part in the phenomenon of h^'persus- 
ceptibilit}". 
Guinea pigs ma}" be sensitized with the filtrate obtained from horse 
serum after precipitation with ammonium sulphate. 
Formaldeh3"d does not appreciabh" infiuence the toxicit3" of horse 
serum and has no effect upon the sensitizing action. 
The sensitizing substance is not dial3"zable through a collodion sac. 
The toxic principle is not altered by various ferments, such as taka- 
diastase, pancreatin, rennin, m3"rosin, invertin, emulsin, pepsin, inglu- 
vin, malt, or papain, nor h3^ certain alkaloids, such as atropin, str3'chnin, 
morphin, or caffein; it is also not altered b3" calcium chlorid, sodium 
I ' nitrate, sodium chlorid, magnesium sulphate, or ammonium sulphate, 
j Guinea pigs sensitized with horse serum do not react to the second 
injection of other proteid substances such as peptone, extract of peas, 
egg albumen, and milk. Converseh", guinea pigs sensitized with sub- 
cutaneous injections of these substances do not react to a subsequent 
j ^injection of horse serum. 
I . Guinea pigs show cpiite as high a degree to susceptibilit3" to cattle, 
I jheep, hog, dog, and cat serum as the3" do to horse serum. 
^ Guinea pigs are quite susceptible to injections of hemoglobin, egg 
Ibumen, milk, or the extract of peas when given two injections with 
^ n interval of at least ten da3"s. Simpler albuminous substances, such 
^ s peptone, seem to have slight sensitizing and poisonous properties, 
hile lower nitrogenous compounds such as leucin and tyrosin possess 
me at all. 
1 The reaction following a second injection of proteid matter in the 
I : ce} pjg, appears to be common to all the higher forms of albumi- 
is substances, no matter from what source, 
j Chis phenomenon of h3'persusceptibilit3^ in the guinea pig ma3" be 
: ful as a ph3^siological test to distinguish true proteid substances 
1 n the lower forms of nitrogenous compounds. 
( 65 ) 
