[2] In 1876, he suggested a hypothesis in explanation of heredity, resembling the germ plasm theory subsequently elaborated by August Weismann, to the effect that the germinal protoplasm retains its specific properties from generation to generation, dividing in each reproduction into an ontogenetic portion, out of which the individual is built up, and a phylogenetic portion, which is reserved to form the reproductive material of the mature offspring.

[1] In Die Entdeckung der Seele[3] ("The Discovery of The Soul", 1878), Jäger advanced the first crude version of the pheromone concept.

His postulated skin, "anthropines," popularly dubbed as "lust compounds," came astoundingly close to reality but the idea was too far ahead of the possibilities of chemistry and the life sciences at this time to be corroborated by experiments.

The system of clothing associated with his name originates from Die Normalkleidung als Gesundheitsschutz[1] ("Standardized Apparel For Health Protection" (1880)), wherein he advocated the wearing of rough fabrics, such as wool, "close to the skin," objecting especially to the use of any kind of plant fibre.

From the 1860s on, Jäger immersed himself in popularizing science through print media, associations, and the founding of a public aquarium and small zoo in Vienna.