Final answer:
Lazzaro Spallanzani (B) was not involved in the 19th-century advancements in public health, unlike Lister, Semmelweis, Nightingale, and Snow who made significant contributions.
Step-by-step explanation:
The person from the choices provided that was not involved in improving public health in the 19th century is B) Spallanzani. The other individuals are known for their contributions to public health and the understanding of disease during that time. Joseph Lister is notable for developing antiseptic procedures in surgery. Ignaz Semmelweis advocated for handwashing to prevent disease transmission. Florence Nightingale's work laid the foundation for modern nursing and emphasized the importance of sanitary conditions in hospitals, and John Snow is considered one of the fathers of modern epidemiology due to his work tracing a cholera outbreak to contaminated water.