The sharing of vaccines was not only a question of collegiality and medical ethics, but a basic requirement for sustaining vaccinations. By transmitting the vaccine to nearby regions, one could create reservoirs for retransmission in case the process was interrupted. Kasahara Hakuō was aware of the practical benefits of sharing and also hoped to save as many children as possible by achieving maximum coverage. In early 1850, he wrote in a letter about his goal of bringing this “incomparable great method to the entire country, without omission.” [Hakushinki, 1850, 1/17, kakitori, attached to previous document, Copy of the kakitori to be sent together with the letter to physicians of nearby domains, p. 55-56]

Given these aspirations, one might expect Hakuō to have liberally shared the vaccine, but this was not actually the case. The town doctor carefully documented the path of the vaccine and tightly controlled the process of sharing. For different reasons, Fukui domain and the vaccinators were interested in maintaining some control over the flow of this biological substance from body to body. Because Hakuō hoped to pass on the vaccine to physicians of other domains, he constructed a trans-territorial network of vaccinators, which used control of medical knowledge to control the transmission of the vaccine. This pathway explores the process and conditions of sharing by following a number of early instances in which Hakuō shared the vaccine with physicians outside his domain territory.