1. It is shown in 52 experiments upon rabbits that the purified gonadotropic hormone has no antigenic function—as an antigen or a haptene—either in the form of prolan derived from the urine of pregnant women or in the form of prosylan, derived from the blood of pregnant mares.

2. The experiments reported elsewhere which ascribe an antigenic structure to prolan, are due to confusion with the so called non-specific urine antigen (urine colloid).

3. Sera of rabbits which are abundant in prolan antihormone (Collip) also contain no antibodies against prolan. The antihormones against the gonadotropic substances must accordingly be considered as protective ferments (Abderhalden).

4. The employment of castrated animals has no influence upon the above results.

5. The lack of immunizingly effective components in pure prolan and prosylan (a) inhibits the possibility of serological diagnosis of pregnancy for the diagnostician; (b) protects the therapeutist against undesirable toxic and allergic secondary effects in intensive prolan treatment. The latter also is valid for pure prosylan preparations.

6. No prolan antibodies could be found in the blood of pregnant women in the 2nd and 4th month of pregnancy, or 1 day and 1 month postpartum.

7. Antihormone against prolan of human origin has no paralysing effect upon a prosylan preparation derived from the blood of pregnant mares (antex); there exists therefore a species specificity.

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