There are several undesirable features in the original Wassermann technic of the complement fixation test for syphilis, as well as in the Noguchi modification, some of which may be sources of error.
In the original Wassermann technic the presence of variable amount of natural antisheep amboceptor, which is found in all human sera, may lead to error, unless removed by the tedious method of bringing in contact with sheep cells. Another objection to the original Wassermann is that unless a sheep is kept in the animal rooms of the laboratory it is sometimes difficult to secure corpuscles for the test, while the keeping of a sheep is more or less expensive, and in some laboratories well nigh impossible.
In the Noguchi technic the use of a non-inactivated serum might, theoretically, be a source of error, although practically, owing to the small amount of serum used, probably is not. But
THOMPSON LO. A MODIFIED WASSERMANN. Arch Intern Med (Chic). 1913;XI(5):512-516. doi:10.1001/archinte.1913.00060290046005